Feeding and advancing the material in the machine tool is an operation that requires maximum precision if the work is to be performed correctly. Otherwise, the machine could be damaged or the material processed in a defective manner.
Transport devices are known comprising two parallel rolls, compressing the material between them and driven to rotate in opposite directions, causing the material to advance by friction.
A drive motor is connected to one of the rolls, which transmits its motion to the other roll through a set of two gears keyed to their shafts. One of the rolls is transversely displaceable, i.e. in a direction essentially perpendicular to that in which the material is advanced, so that it can be moved away from the other roll to allow the material to be inserted or to release the material when it is engaged by those elements of the machine which position and guide it as it is processed.
Of course, the distance between the rolls is determined by the thickness of the material being processed and the desired clamping pressure, which is in turn determined by the nature of the material and/or its surface quality.
U.S. Pat. No. 2,783,996 and German Patent 30 00 639 describe this type of device, in which the transversely movable roll is supported by a chassis forming a cover and articulated on a shaft mounted parallel to those of the rolls, with the rotational link between the two rolls being provided by an even number of gears, at least four, one of which is keyed to each shaft of the roll, one being freely supported by a shaft coaxial with the shaft on which the chassis is articulated, and one intermediate gear meshing with the one mentioned above which is free to rotate, and with one of the two gears keyed to the roll shafts.
The design shown in U.S. Pat. No. 2,783,996 does not provide suitable means, jacks for example, to press the movable roll against the material held between the two rolls, nor means for sufficiently separating the rolls to feed the material. The result is a significant lack of precision in feeding the material and in releasing it.
The design shown in German Patent 30 00 639 provides a chassis pivoting on a shaft whose height is adjustable, a jack to move the rolls apart or closer together by exerting a pressure on them, and a cam which abuts the chassis to release the material. This device has the disadvantage of being complicated to manufacture and inaccurate to regulate as regards the spreading of the rolls and the releasing operation, due to the forces exerted on the chassis and the shaft on which it pivots.